This invention relates in general to fasteners that are used to secure devices to bones in surgical procedures. In particular, this invention relates to a pedicle screw assembly having a retractable screw tip that facilitates the securement of the pedicle screw assembly to a spinal vertebra in a minimally invasive fashion during an orthopedic surgical procedure.
Many surgical procedures involve the securement of a device to a bone. For example, during an orthopedic surgical procedure, it is often necessary to secure a support or alignment device to one or more vertebrae in the lumbar or thoracic region of the spine. The securement of such a device to the vertebra usually involves a series of relatively complex steps. For example, in one known procedure, a conventional Jamshidi needle (which includes a hollow outer cannula and an inner obturator having a tapered cutting edge) is initially inserted through a relatively small incision until the tapered cutting edge of the obturator engages a desired location on the surface of the vertebra where a fastener, such as a pedicle screw, is to be secured. The precise location where the tapered cutting edge of the obturator engages the surface of the vertebra is usually determined using conventional fluoroscopic or other imaging or navigational techniques.
Once the tapered cutting edge of the obturator has been positioned at the desired location on the surface of the vertebra, a conventional impaction tool is used to advance the Jamshidi needle further within the vertebra so as to create a passageway therein. The depth of the insertion of the Jamshidi needle within the vertebra can be determined using conventional fluoroscopic or other imaging or navigational techniques. Then, the obturator is removed from the Jamshidi needle, leaving behind the hollow outer cannula. A flexible guide wire is next inserted through the hollow outer cannula of the Jamshidi needle until the leading end thereof extends through the passageway and is received within the body of the vertebra at a desired depth. The depth of the insertion of the leading end of the guide wire within the body of the vertebra can be determined using conventional fluoroscopic or other imaging or navigational techniques. Then, the hollow outer cannula of the Jamshidi needle is withdrawn from the vertebra, leaving the leading end of the guide wire within the body of the vertebra.
A conventional cannulated threading tool is next inserted over the trailing end of the guide wire and guided therealong to the relatively short passageway in the vertebra. The threading tool is used to tap a thread within the passageway in the vertebra. The depth of the thread that is tapped within the passageway can be determined using conventional fluoroscopic or other imaging or navigational techniques. Next, the threading tool is withdrawn, and a cannulated pedicle screw is inserted over the trailing end of the guide wire. The pedicle screw is guided along the guide wire until a threaded tip of the pedicle screw is guided to the tapped passageway in the vertebra, again using conventional fluoroscopic or other imaging or navigational techniques. The pedicle screw is secured to the vertebra by rotating it about the guide wire with a conventional tool, which causes the threaded tip of the pedicle screw to thread within the tapped passageway in the vertebra. Such rotation is continued until the pedicle screw has been driven a predetermined distance into the body of the vertebra that, again, can be determined using conventional fluoroscopic or other imaging or navigational techniques. Lastly, the guide wire is removed, leaving the pedicle screw secured to the vertebra, to which the support or alignment device can be secured.
Although this procedure for securing a conventional pedicle screw to a vertebra has functioned satisfactorily, it can be seen that the fluoroscopic or other imaging or navigational techniques are frequently employed, which is time consuming and can result in significant radiation exposure. Thus, it would be desirable to provide an improved structure for a pedicle screw or similar fastener that avoids these issues.